Magnetic tape cartridges of the "cassette" type met with instant public acceptance following their introduction in the early 1960's and, in the ensuing years, have created one of the largest and fastest growing industries in the world with expected sales for the year 1971 approximating upwards of 1 billion units. The compact unit-handled characteristic of these cartridges coupled with their excellent audio reproduction qualities, low cost and capability of being concomitantly erased and re-recorded make them ideally suited for such diverse uses as entertainment, education, business communications and the like. Although the great majority of cassette cartridge sales are of unrecorded tape for subsequent home recording by the user, there is a very substantial, and fast growing, market for pre-recorded cassettes.
A typical cartridge tape may include a double track system whereby the full tape length may be played or recorded along one-half the tape width in one direction after which time the cartridge may be reversed and the remaining half tape width played or recorded as the tape is transported in the other direction between selectively driven reels. Double track tapes of this type typically provide program lengths up to 90 minutes which, as will be apparent, may include a large number of separate recordings which are normally spaced by ten second unrecorded, or audio pause, intervals when the tape is running at normal record or playback speed. The machines which play these tapes are provided with high speed forward and rewind controls for quickly advancing or rewinding a tape to the desired program selection and it is the fast and accurate location of the audio pause intervals immediately prior to selected ones of the plurality of recorded programs that comprises the subject matter of the invention.
Prior methods of locating audio pause intervals within the total length of recorded tape have included footage counting instrumentation requiring special equipment which is both expensive and impractical for use with "cassette" type cartridges; a relatively accurate but prohibitively expensive system of splicing colored pieces of plastic or paper into the tape reel; a reflection viewing system employing a movably mounted mirror to constantly reflect cue markings applied on the non-recorded tape surface through the viewing window; and the most common and least expensive but highly inaccurate system involving the placement of an index adjacent the viewing opening whereby the tape diameter may be estiminated by visual comparison with the index. Because of the very high volume of "cassette" type cartridge sales and their relatively low selling cost it is apparent why inexpensive indexing systems are required.
"Cassette" type cartridge tapes are transported between their selectively driven reels with the tape recording surface facing outwardly relative to the cartridge housing and reel axes so that the recording surface will be in position to engage the playback/record and erase heads as conventionally positioned in the playback and recording machines with which the cartridges are used. Consequently, the recording surface faces outwardly as it is wound between the reels and may be seen through the conventional viewing window as the tape is being reeled in either direction. Although the placement of cue or index markings, in the form of ink, dye, paint or other like indicial markings on the recording surface over the non-recorded audio pause intervals would provide an excellent method of enabling one to directly view these cue markings for the determination of a particular selection along the tape length; the presence of such markings on the recording surface would render the tape unusable for subsequent recordings since such markings diminish the recording properties of the tape. Inasmuch as the great majority of cartridge tapes are destined to be used for multiple erasures and recordings it is apparent that the presence of cue markings on the originally recorded surface is an impractical approach to the problem.
Inasmuch as any finite tape interval will never occupy the precise same radial position with respect to its supporting reel axis upon successive windings due to inherent reel and/or tape slippage and variations in winding tensions applied to the tape; it is apparent that a particular tape interval cannot be located with reproducible accuracy as a function of wound tape diameter. Such locating systems involving index markings on the cartridge housing, at best, provide nothing more than a rough estimation of tape interval locations and then only if the particular index marking to be associated with the wound reel diameter has been previously noted and recorded as on the outer cassette housing. Nevertheless, this highly inaccurate locating system is the only one presently in widespread use since it represents an acceptable compromise on the basis of cost and assembly procedures as among the aforenumerated systems. Thus, both the tape splice and reflection viewing systems provide absolute reproducible accuracy of tape interval locations since tha tape, itself, is cue marked and the relationship of the marks to the desired intervals are independent of variations in reel diameter upon subsequent windings. The tape splice system, however, involves a physical alteration of the tape which is not only a fairly expensive process but renders that particular portion of the tape unsuitable for subsequent recordings while the reflection viewing system involves an alteration of cartridge assembly procedures and introduces an additional moving part thus increasing the likelihood of tape fouling.
The primary purpose of the invention is to provide a tape cueing system that combines the reproducible accuracy of the reflection viewing system with the simplicity of the index comparison viewing system while requiring no alteration whatsoever of a conventional tape cartridge and not affecting subsequent tape recording over the cue marked portions of the tape.